Group psychosocial programs may improve mood and increase support for prostate cancer patients. Some studies show benefits for patients experiencing distress and no benefit for those with low/no distress, yet patients are typically enrolled in trials regardless of any demonstrated need for an intervention. Programs including only those with distress may better address patient needs. Researchers have varying opinions about conducting programs with homogeneous groups of distressed patients since non-distressed patients may be needed to model adaptive coping. Though well-validated theoretical models including Social Comparison Theory (SCT) support this view, no research has been specifically designed or adequately powered to examine whether distressed patients benefit from the presence of non-distressed patients and whether non-distressed patients benefit from participation. According to SCT, cancer patients prefer evaluating themselves against less fortunate others to increase self-esteem and manage mood, and concurrently, prefer obtaining information from and affiliating with more fortunate others to learn adaptive coping. A heterogeneous support program (distressed and non-distressed patients) provides distressed patients maximal opportunity for preferred social comparisons;a homogeneous program (distressed patients only) does not. For non-distressed patients, opportunities for preferred social comparisons may be limited, creating the possibility for no or even negative effects on psychosocial functioning and quality of life (QOL). The purpose of this research is to examine the effect of group composition on psychosocial program efficacy for prostate cancer patients and evaluate whether programs are more efficacious for distressed patients when implemented in a heterogeneous versus a homogeneous group. The efficacy of the heterogeneous group for non-distressed patients also will be examined. Prior to the larger trial powered to address these questions, this feasibility study will be conducted with 90 prostate cancer patients (60 distressed and 30 non-distressed). Distressed patients will be randomized to a 3-month psychosocial program in a heterogeneous group or the same program in a homogeneous group. The aims are to: 1a) collect feasibility and process evaluation data;1b) develop estimates of the percentages of distressed patients and of those high and low in social comparison orientation;2a) obtain estimates of the effect sizes for distressed patients in both groups on psychological functioning and QOL at 3 months;2b) estimate the effects on distressed patients in both groups on hypothesized SCT-mediators at 3 months;2c) explore changes in distress in the non-distressed patients in the heterogeneous group;and 2d) explore differences in distressed and non-distressed patients on measures of social comparison and examine changes in these measures for both following participation in the group program. PUBLIC HEALTH RELEVANCE: This research may indicate that to address the needs of patients experiencing psychosocial distress, groups may be most efficacious when they comprise members experiencing mixed distress levels. If these heterogeneous programs prove harmful or offer no benefit to non-distressed patients, ethical issues emerge regarding their referral to support groups. Findings may suggest a modification to current research and clinical practice wherein non-distressed patients remain as participants, yet are properly trained to maximize benefit for distressed patients and minimize negative consequences for themselves.